Conventional output drivers used to convert a low voltage input signal to higher voltage output signal are needed because the transistor operating voltage varies between newer technology integrated circuits and older technology integrated circuits. One solution for building these type of drivers is to use high voltage transistors. This has the drawback that the integrated circuit with the driver then has to have both thick oxide circuits and thin oxide circuits. This results in higher production costs. In addition, these types of driver circuits have reduced switching speed at slow PVT (Process Voltage Temperature) conditions and high noise at fast PVT conditions, because of constant rail to rail gate to source transistor voltage.
Another solution has been to use thin oxide circuits with low voltage transistors. This reduces the production costs. However, this solution requires a bias-p signal and bias-n signal to protect the gate oxides of the transistors. The bias-p signal is set to the difference between the high voltage external IO (Input/Output) power supply and the low voltage internal regulated power supply and the bias-n signal is the low voltage internal regulated power supply. As a result this driver circuit will work with low voltage transistors, but still has reduced switching speeds at slow PVT (Process Voltage Temperature) conditions and high noise because of overdrive conditions at fast PVT conditions, because of the constant gate to source transistor voltage.
Thus there exists a need for driver circuit that does not have reduced switching speed at slow PVT (Process Voltage Temperature) conditions and does not introduce excessive noise at fast PVT conditions.